Rubber treatment



United States Pate r-RUBBER TREATMENT Kenneth W. Doak, Bloomfield,"N.J.,"assignor"to United -tion of New Jersey *No Drawing. Application November 16, 1953,

' Seriai'No. 392,484

10. Claims. (Cl. can-41.5

This invention relates to improvements in the technique of processing. high carbon black-rubber mixes prior to vulcanization thereof, and :morepar'ticularly to improvem'ents in iso called low hy steresis processing of mixture's'of carbon black and rubber.

The technique ofprocessinghigh carbonblack and "rubber mixes prior to vulcanization thereof, whereby to obtain v'ulca'nizates with .improvements in "physical and chemical iproperties, is described lin Gerke;et a1. U; 8.1-1.

per 100 parts by weight of rubber,-and then-subjecting a "substantially "homogeneous mixture of the ingredients ":to I arheat treatment at :a temperature:substantially above 250 '.F., :'.the .preferredtemperature:being in'the .range from. about 300.-F..-to 370 F., andrna'sticating the mix during and/or after such heattreatmentgor. alternately therewith. The duration of the special heat treatment may vary with the temperature employed, the higher the :aemperature the sshorter the "time; and :is governed. also 3 by the :degree ofi change-desired in the; properties: of the ultimate vulcanized product which: propertiesr are-"gauged rto bezcompatible .with its final-ruse. :In rgeneral heat 1 treatments -'of ffrom 1 1-0 t to 60 minutes: duration 1 will "be rfoundrsuitable for .most; purposes;-:an'd particularly within the' preferred temperature range.

"An object 50f the present: invention isi-to zprovide "new chemical tpromoters i for zthe processing of 1 rubber :and rcarbonssblack'mixes. as described in USSpP. 2,118,601 -.whereby:to obtainzihigh electricalfresistance and IOWftOI- -.sionalrhysteresis of itreadzstocks. :Afurther objectisfio provide :substantial: decreases-in the. time.of the low-hye teresis processing by..the;use:of.the therein disclosed chemicals with consequent increase in the capacity and output of equipment. Other objects will appear more fully hereinafter.

"I'thaVeTouridIthat aromatic sulfonyl chlorides substantiallyidecrease the time andtemperature for low hys- -teresi's processing. ZDhese aromatic =sulfonyl chlorides may be representedby RSOzCl, where R is a phenyl or naphthyl group or a :phenyl or naphthylgroup substituted by one or more alkyl groups, nitro groups, acetyl amino;.'groups, festerrgroups,"or halogens. .ISpecificiexamplesofftheseaaromatic su'lfonyl chlorides are: benzene:

sulfonylchloride, p'-toluene'sulfonyl;chlonide o toluene: I sulfonyl chloride, p-nitrobenzenesulfonyl -;chloride,-1 2',5-1-

dichloro'benzenesulfonyl chloride, 4-acetylaminobenzenedichlorobenzenesulfonyl chloride, 1,3-dimethylbenzene- "-2 4-sul-fonyl chloride, naphthalene beta sulfonyl chloride,

and naphthalene-alpha-sulfonyl chloride.

Thesepromoters are-effective in natural rubber, synqthetic: rubbery homopolymers of aliphatic conjugated. .di- 5 olefin hydrocarbons,especially butadiene and isoprene,

1 and-synthetic rubbery copolymers of r such wdiolefin hydrocarbons with copolymeriza'ble monoolefinic com- -;pounds, Slh -as isobutylene, styrene, alpha-methyl a .styrene, ethyl acrylate acrylonitrile, methyl methacrylate, 10 :m-ethylacrylate, methyl vinylketone, methyl is'opropenyl ketone -and mono-vinyl pyridines. They are. particularly .eiiective in natural rubber, incopolymers of amajon proportion, typically from 90m 995, of isobutylene Iand a minor, proportion, typically correspondingly from 10. to 0.5 of an aliphatic conjugated diolefinhydrocarbon, especially :buta diene or isoprene (known commercially :as Butyl-ri1bber),-and incopolymers of butadiene and styrene, (known as GR*S) iihe process of any invention comprises mixing natural rubberor a-synthetic rubbery polymer of analip'hatic conjugated diolefin, i.- e., an aliphatic conjugated. diolefin homopolymer or-copolymer, with a relatively -large amount of a rubber-reinforcing carbon black and a relatively small but effective amount, typically from 1 to 3 par-ts per '100 parts of rubbery material, 'ofan aromatic wsulfonyl chloride,.and heatingthis mixture at'a-temlpera'ture offrom 275 F. ."to atemperature 'justshor-t ofi that'=-at which thesru-bber wouldtbe injured, to bring "about the :desired changes in the rubber-and=carbon i black-mixture -whereby a vulcanizate of Ithisi mixture will have a 'considera-bly reduced torsional -':hysteresis and a considera'bly increased electrical resistivity. Thisftheat treatmentiscarried out in the: absence or vulcanizing agents, e. g., sulfur or sulfur-yieldingcompounds. Following Ithe heat treatm'ent, thevulcanizing and other desired. compounding ingredients including conventional accelerators-iandithe like are intimately incorporated in the 'conventional'imanner, after which themixture is shap'ed. and vulcanized in the usual way. 40 Any carbon.blackwhich is capable: of reinforcing the rubber. can tbe used in the practice of my invention. I u-sually use leitheria' furnace "bl-acksor' a channel .black. Those :skilled in the art :will "appreciate that the :type sof black isl oi ten selected-with' reference to .theiiparticular rubber employed. The amount of carbon black present during the heat treatment shoul'd'be equal to at least -25:parts;'=per-100 parts by weight of rubber. Preferably thesarnount of carbon black is equal to at least 40 parts per'l-OO parts ofrubber, the-use of-such high proportions 0f carbon blackbeing particularly desirable in the case of tread stocks. The amount "of carbon black present duringtheheat treatmentcan "be "as "great as 100 parts -per-'I00 pa'rts' of' 'rubber.

In the'preferred practice I of my invention, the-heat treatment -of the"mixtureof rubber, carbon black and aromatic sulfonyh chloride -is=carried out by mastication at temperatures in the range of 275-400" F., and more preferably in the range of 300-400 F., with any suitable type of masticatiug equipment such as an open two-roll rubber mill or more preferably an internal rubber mixer, especially a Banbury mixer. The Banbury mixer is particularly advantageous because it exerts a severe masticatory action upon the charge and because it conserves the-heat generated by the mixing action and this heat sfifi greatly-raids in elevation of the stock temperature to withirr -thedesired range. Depending upon the size and operating'speed of the Banbury mixer, and other factors, extraneous heat may or may not need to be applied to .bring-t he stock temperature within the desired temperaturev range and to hold it there. If desired, extraneous cooling may be applied to keep the temperature from rising above the desired level.

The optimum duration of the heat treatment will vary depending upon many factors, including the temperature of heat treatment, type of heat treatment, i. e., whether it is static or dynamic, type of equipment used, c. g.,

7 4 60 minutes, at temperatures of 325-350 F., would be required to obtain the above results.

EXAMPLE 2 in the case of masticatory heat treatment whether an 5 An experiment is Carried out in a manner i n i open rubber mill or a Banbury or other type of internal with that of Example 1, except that Parts of 1 mixer i d, amount f ti sulfonyl hl id d, enesulfonyl chloride or 2.0 parts benzenesulfonyl chloride etc. In any event, the treating time will be considerably is used in Phice of the p-hitloheflzehesulfohyl chlol'hieshorter, at given temperature conditions, than the time The following results are Dhtailledi required when the aromatic sulfonyl chloride is omitted. 10

In the case of the preferred masticatory treatment, times Log 30- Tore.

' of the order of 5 to 30 minutes will generally be adequate 515m? ga t; for the purposes of my invention, the longer times being used at the lower temperatures and vice versa. It is 79 0 121 well known that different rubbers vary as to the highest Sample with g-tuluenesulfonyl chloride 12:4 1091 temperatures they can withstand without harm and the 58mph with time and temperature should of course be so regulated as to not impair the properties of the final vulcanizate. EXAMPLE 3 It is preferable to form an intimate mixture of the Two parts f Ptoluenesulhnfl chloride is added to a rubber, carbon black and aromatic sulfonyl chloride at masterbatch f 100 parts f a butadiene stymne l a relat1vely low temperature, 1. e., below 275 F., in (GR S polymerized in emulsion at 4 E) 5 ordento avoid premature reaction of the aromatic sulfonyl Parts f carbon black (a medium processing channel chloride whereby its promoting effect upon the low black), 6 Parts f hydrocarbon oil and one Part f stem-i6 hysteresis processing would be serlously reduced. acid High temperature mastication is carried out in a The following examples illustrate the preferred methods laboratory Banbm-y mixer f 6 minutes at 25 F. of practicing the invention. All parts are by weight. Th ft r 3 pal-ts f Zinc oxide 1 pal-t f Lineman)- EXAMPLE 1 benzothiazole, 0.4 part of diphenylguanidine, and 2 parts A masterbatch is prepared by mixing together 100 parts 9 sulfur mcorpprated on a P The Stock Hevea rubber, 50 parts carbon black (a medium procif i g i at AS a control an essing channel black known as Spheron-6) .and 5 parts 1 entlc master am Is treate 3 game manner stearic acid. This mixing operation is carried out in Capt that no p'toluenesulfonyl c londe 15 used The the conventional manner in a Banbury mixer or a two sults'are Shown below roll rubber mill. To 155 parts of this masterbatch is added 2.2 parts p-nitrobenzenesulfonyl chloride on a two $535 55 roll rubber mill at a temperature preferably below 275 230 1 F. The mill temperature is then raised to 300 F., and the mixture is masticated for ten minutes. Thereafter Sample with p-toluenesult'onyl chloride 12.7 0.098 the min is cooled to 150-200 F. and 2 parts of pine tar, e5 2 parts of zinc oxide, 1 part of antioxidant, 1 part of 40 accelerator, and 2.6 parts of sulfur are incorporated. P-toluenesulfonyl chloride thus reduces the torsional The mixture is placed in a suitable mold and vulcanized hysteresis and increases the specific electrical resistivity minutes at 287 F. As a control an identical masterof a mixture of carbon black and a rubbery copolymer of batch is prepared and subjected to all the previously debutadiene and styrene (GR-S). scribed manipulative steps except that no p-nitroben- 5 zenesulfonyl chloride is added to the mixture. The spe- EXAMPLE 4 cific electrical resistivity and torsional hysteresis are de- A m asterbatch is prepared by mixing in a conventional termined for the two vulcanizates, with the following manner 100 parts of an isobutylene-isoprene copolymer results: (kn own commercially as Butyl-IS) and parts of 50 carbon black (a medium processing channel black). Varggg sious aromatic sulfonyl chlorides are added to portions 151 of the masterbatch 'at 150-275 F. The mixtures are then masticated at a high temperature in a laboratory Control 7,2 2 Banbury mixer for 15 minutes. Thereafter, 3 parts of Sample with p-nitrobenzene-sulfonyl chloride"-.. 13. 0 '0. 061 t i id 3 -t f i id Que t f t th L thiuram disulfide, 0.5 part of Z-mercaptobenzothiazole, The practice of the invention thus increases the specific and 2 parts of sulfur (per 100 of rubber) are incorporesistivity by a factor greater than 600,000, and reduces rated in each mixture on a two-roll mill at a temperature the torsional hysteresis at 280 by over 50%. of 150-200 F. The stocks are vulcanized minutes at In the absence of a chemical promoter, times of 30 to 1 293 F. The data are summarized in Table II.

Table 11 Time Tom. Temp., of Hyst. ML-4 Chemical Used Parts F. Maatt- LOgR 280F (raw) cation,

min.

None (control) 375 16 0.3 .195 74 -Toluenesultonyl chloride 1.6 375 16 134) .099 61 p-Nitrobenzeuesnllonyl chloride.... 1.6 300 15 6.7 .268 Do 1.5 325 15 12.2 .117 v as 30s-... 1.5 350 15 12.0 .113 as Do 1.5 375 15 12.4 .105 5a Naphthalene-beta-sultonyl chloride. 1.5 375 15 12.6 .109 66 VI Mooney viscosity, large mtor, 4' at 212 F. p

Table II shows that aromatic sulfonyl chlorides reduce the torsional hysteresis and increase the specific electrical resistivity of mixtures of carbon black and a copolymer of isobutylene and isoprene (Butyl rubber). It will be seen that the higher temperatures, i. e., 325 F. or above, are more effective in the case of Butyl rubber.

Although I have disclosed my invention with particular emphasis upon the preferred practice wherein the heat treatment is accompanied with mastication, nevertheless my invention can be practiced by carrying out the heat treatment under static conditions. For example, I may intimately mix the rubber, carbon black and aromatic sulfonyl chloride in any suitable manner and then heat this mixture at 275-400 F. Without simultaneously masticating it, the heat-treated mixture being subsequently masticated and compounded with conventional compounding and vulcanizing ingredients followed by shaping and vulcanizing in the usual way. The static heat-treatment can be conducted by placing slabs of the stock in an oven heated to a suitable temperature, or slabs of hot stock can be stacked up and allowed to stand for several hours, preferably under relatively non-heat-conductive conditions, in order to maintain the mixture at the temperature of 275-400 F. for as long as reasonably possible. If desired, the slabs can be wrapped with a suitable insulating blanket to cause prolonged retention of heat. Such static heat-treatment has the advantage of releasing the Banbury equipment from use for carrying out the heattreatment and this may be desirable under certain conditions.

The electrical resistivity values given in the above examples were determined by measuring the resistance of a specimen of known thickness (about 0.1 inch) placed between mercury electrodes, under a potential difference of 135 volts, using a sensitive galvanometer with an Aryton shunt. The logarithm (to base of the specific electrical resistivity (expressed in ohm-ems.) is designated Log Resistivity.

The torsional hysteresis figures represent the logarithmic decrement (to base 10) of the observed amplitudes of successive oscillations of a torsion pendulum, measured at 280 F. with an apparatus consisting essentially of a torsion pendulum in which the sample of rubber tested supplies the restoring force when the pendulum is defiected. For further description of this test see Gerke et al., 2,118,601.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A process which comprises mixing rubber selected from the group consisting of natural rubber and synthetic rubbery polymers of aliphatic conjugated diolefins with a relatively large amount of rubber-reinforcing carbon black and from 1 to 3 parts, per 100 parts of said rubber, of an aromatic sulfonyl chloride having the formula R-SOzCl, where R is selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl substituted by at least one alkyl group, nitro group, acetylamino group, ester group, and halogen, heating the mixture at a temperature of at least 275 F. but below that at which the rubber would be harmed, thereafter incorporating wilcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

2. A process which comprises mixing rubber selected from the group consisting of natural rubber and synthetic rubbery polymers of aliphatic conjugated di-olefins with a relatively large amount of rubber-reinforcing carbon black and from 1 to 3 parts, per 100 parts of said rubber, of an aromatic sulfonyl chloride having the formula 1140201, where R is selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl substituted by at least one alkyl group, nitro group, acetylamino group, ester group, and halogen, masticating the mixture a temperature of from 275 to 400 F., thereafter incorporating vulcanizing and other desired ingredients,

6 shaping the mass, and vulcanizing the resulting shaped mass.

3. A process which comprises mixing natural rubber "with a relatively large amount of a ,rubber reinforcing carbon black andfnoml to 3 parts, per partsof said rubber, of an aromatic snlfonyl chloride having the formula R-SOzCl, where R is selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl substituted by at least one alkyl group, nitro group, acetylamino group, ester group, and halogen, masticating the mixture at a temperature of from 275 to 400 B, thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

4. A process which comprises mixing a rubbery copolymer of butadiene and styrene with a relatively large amount of a rubber-reinforcing carbon black and from 1 to 3 parts, per 100 parts of said copolymer, of an laromatic sulf'onyl chloride having the formula R-SO2Cl, where R is selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl substituted by at least one alkyl group, nitro group, acetylamino group, ester group, and halogen, masticating the mixture at a temperature of from 275 to 400 F., thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

5. A process which comprises mixing a rubbery copolymer of isobutylene and an aliphatic conjugated diolefin with a relatively large amount of a rubber-reinforcing carbon black and from 1 to 3 parts, per 100 parts of said copolymer, of an aromatic sulfonyl chloride having the formula RSO2C1, where R is selected from the group consisting of phenyl, naphthyl, and phenyl and naphthyl substituted by at least one :alkyl group, nitro group, acetylamino group, ester group, and halogen, masticating the mixture at a temperature of from 325 to 400 F., thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

6. A process which comprises mixing natural rubber with a relatively large amount of a rubberreinforcing carbon black and from 1 to 3 parts of p-nitrobenzene sulfonyl chloride per 100 parts of said rubber, masticating the mixture at a temperature of from 275 to 400 F., thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

7. A process which comprises mixing natural rubber with a relatively large amount of a rubber-reinforcing carbon black and from 1 to 3 parts of p-toluenesulfonyl chloride per 100 parts of said rubber, masticating the mixture at a temperature of from 275 to 400 F., thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

8. A process which comprises mixing a rubbery copolymer of butadiene and styrene with a relatively large amount of a rubber-reinforcing carbon black and from 1 to 3 parts of p-toluenesulfonyl chloride per 100 parts of said copolymer, masticating the mixture at a temperature of from 275 to 400 F., thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

9. A process which comprises mixing a rubbery onpolymer of isobutylene and an aliphatic conjugated diolefin with a relatively large amount of a rubberreinforcing carbon black and from 1 to 3 parts of p-toluenesulfonyl chloride per 100 parts of said rubbery copolymer, masticating the mixture at a temperature of from 325 to 400 F., thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and vulcanizing the resulting shaped mass.

10. A process which comprises mixing a rubbery c0- p-olymer of isobutylene and an aliphatic conjugated diolefin with a relatively large amount of a rubberreinfprcing carbon black and from 1 to 3 parts of p-nitrohenzenesulfonyl chloride per 100 parts of said rubbery copolymer, masticating the mixture at a temperature of from 325 to 400 F., thereafter incorporating vulcanizing and other desired ingredients, shaping the mass, and 5 vulcanizing the resulting shaped mass.

8 References Cited in the file of this patent UNITED STATES PATENTS Gerke et a]. May 24, 1938 

1. A PROCESS WHICH COMPRISES MIXING RUBBER SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER AND SYNTHETIC RUBBERY POLYMERS OF LIPHTIC CONJUGATED DIOLEFINS WITH A RELATIVELY LARGE AMOUNT OF RUBBER-REINFORCING CARBON BLACK AND FROM 1 TO 3 PARTS, PER 100 PARTS OF SAID RUBBER, OF AN AROMATIC SULFONYL CHLORIDE HAVING THE FORMULA R-SO2C1, WHERE R IS SELECTED FROM THE GROUP CONSISTING OF PHEYL, NAPHTHYL, AND PHENYL AND NAPHTHYL SUBSTITUTED BY AT LEAST ONE ALKYL GROUP, NITRO GROUP, ACETYLAMINO GROUP, ESTER GROUP, AND HALOGEN HEATING THE MIXTURE AT A TEMPERATURE OF AT LEAST 275*F. BUT BELOW THAT AT WHICH THE RUBBER WOULD BE HARMED, THEREAFTER INCORPORATING VULCANIZING AND OTHER DESIRED INGRIDENTS, SHAPING THE MASS, AND VULCANZING THE RESULTING SHAPED MASS. 